"The Natural Philosopher" wrote in message
...
dennis@home wrote:


"The Natural Philosopher" wrote in message
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I think the biggest problem would be air flow caused by passing
trains.. you would probably need to build a central wall to control it.
This would also make it much stronger.

No it wouldn't dennis.

A circular cross section is already as strong as it can be assuming
adequate wall stiffness to stay inside Euler instability criteria.


More BS.. that assumes uniform pressure, something you seldom get.

shows how little you now about deep tunnelling and the behaviour of rock
and soil under pressure.
.

Shows that you assume all round tunnels are deep!